1. Field of the Invention
This invention relates to an inorganic fibrous material which is useful as a reinforcement for composite materials and has improved wetting property with respect to metals, plastics or ceramics as a matrix of the composite materials, and to a process for producing the inorganic fibrous material.
2. Description of the Prior Art
Metals, plastics and ceramics reinforced with inorganic fibers such as carbon fibers and alumina fibers as a reinforcing material, known respectively as FRM, FRP and FRC, have attracted wide attention as structural materials having high mechanical strength.
Inorganic fibers used for production of composite materials are required to have high mechanical strengths such as tensile strength and modulus of elasticity and good wetting property with respect to metals, plastics and ceramics as a matrix, and to undergo little degradation by reaction with the matrix.
Carbon fibers have excellent strength and modulus of elasticity, but very bad wetting property with resepct to a matrix such as molten aluminum. Furthermore, carbon fibers tend to react with molten aluminum at high temperatures and cause a drastic reduction in the strength of the resulting composite material. Hence, if the carbon fibers are directly used to reinforce composite materials, the resulting products cannot have the desired mechanical strength.
Some methods have been proposed in an attempt to eliminate the above inconveniences. For example, Japanese Laid-Open patent publication No. 85,644/1980 discloses a method which comprises coating the surface of carbon fibers with a polymeric organosilicon compound such as polycarbosilane, polysilane or polycarbosiloxane, and rendering the polymeric organosilicon compound inorganic thereby to form a ceramic composed mainly of silicon carbide as a surface layer. Japanese Laid-Open patent publication No. 53,728/1984 discloses a method which comprises providing a vitreous layer on the surface of carbon fibers, coating it with a polymeric organosilicon compound such as polycarbosilane, polysilane or polycarbosiloxane, and rendering the polymeric compound inorganic to form a surface layer.
The method of Japanese Laid-Open patent publication No. 85,644/1980 is not satisfactory because the adhesion of the central carbon fiber layer to the surface layer is low and strains remain between the two layers with the result that the fibers themselves have reduced tensile strength and flexibility.
According to the method disclosed in Japanese Laid-Open patent publication No. 53,728/1984, the resulting reinforcing fibers themselves have good mechanical strength, but the wetting property of the carbide forming the surface layer with respect to a plastic or molten metal is not sufficient. Furthermoe, since the carbide has high reactivity with a molten metal such as molten aluminum, a composite material having satisfactory mechanical strength cannot be obtained by using the resulting reinforcing fibers.